Molecular forces study and microstructure and gelling properties of smooth hound protein gels prepared by heat-induced gelation process: Effect of pH variation on textural and functional properties

Smooth hound gels (SHGs) were prepared from the viscera by heat treatment at different pH values (2.0, 5.0, 7.0 and 9.0). Their physicochemical and functional properties, microstructure and molecular forces were investigated. The pH variation was found to influence the protein molecular weight distribution resulting in different gelling properties. According to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) protein profiles, SHG-9 prepared at pH 9.0 contained the greatest amount of high molecular weight proteins. Further, the SHG-9 exhibited the highest gel strength, fracture resistance and elasticity. On the contrary, microstructure and infrared spectra analyses showed that acidic conditions provided gel networks with unarranged secondary structure and a high hydration level, which might be attributed to the formation of hydrogen bonds between polymer molecules. In addition, the molecular forces study showed that the primary dominated intermolecular forces involved in the SHGs were hydrophobic interactions and hydrogen bonds, while the secondary forces included electrostatic interactions and disulfide bridges. These results were confirmed by the levels of free amino acids. Thus, this study identified opportunities to develop high value-added products from fish by-products that might be used to carry out the function of the desired food application. (C) 2016 Elsevier Ltd. All rights reserved.